ABSTRACT ? Project 1 Patient-to-patient variability in response to drugs creates a significant challenge for the safe and effective treatment of many human diseases. Pharmacogenomics seeks to address this challenge by linking drug response to patient genotypes at important loci in order to better customize patient treatments. However, while much progress has been made in this regard in Western and Asian populations, there remain many underserved and minority communities where very little is known about the consequences of pharmacogenetic variation. A widely studied paradigm in this area concerns genetic variation and its effects on warfarin?s anticoagulant drug response. However, much remains to be learned about factors modulating vitamin K- dependent clotting factors that are inhibited by the drug to exert its pharmacological actions. We address these deficiencies here in Aims 1-3 of Project 1 of this Program Project Grant application. In Aim 1 we will perform in vitro metabolic studies with several novel CYP2C9 variants that we identified recently in Alaska Native (AN) populations. Enzyme variants will be recombinantly expressed in several cell lines and their metabolic capabilities assessed through evaluation of transcripts, protein stability and catalytic capabilities towards several CYP2C9 substrate including (S)-warfarin. In Aim 2, a complementary in vivo pharmacokinetic study to Aim 1 is proposed in AN participants who have been genotyped for the new CYP2C9 variants. Subjects will be given the CYP2C9 probe substrate, flurbiprofen, orally and pharmacokinetic parameters measured in urine and plasma from these subjects to fully characterize the functional impact of the most common new variant, CYP2C9 M1L, which is present at a high allele frequency in this population. Tissues obtained in the conduct of Aim 2 will also be used further for lipidomic and metabolomics screening to identify new biomarkers for CYP2C9. Finally, in Aim 3, we will undertake a discovery project involving global gene knockdown in a cell line engineered to produce a clotting factor chimera that enables high-throughput functional analysis. Collectively, completion of these studies will advance our understanding of the pharmacogenomics of hemostasis and establish new risk factors for bleeding in the AN community.